1. Field of the Invention
The present invention relates to a cylinder liner for reciprocating-piston-type internal combustion engines, with the liner of a given cylinder having a ring-shaped or annular insert that narrows the cylinder in a zone opposite the fire land (top land) of the pertaining piston when the latter is in its top dead center position.
2. Description of the Prior Art
The ring-shaped insert, which narrows the top end of the cylinder, is intended to prevent carbon from depositing on the fire land of the piston, since as the fire land slides over those parts of the cylinder (the cylinder liner) that are swept or passed over by the piston rings, such deposits tend to cause local polishing of these cylinder areas. As a result of this "bore polishing", the hydrodynamic lubrication film is disturbed due to insufficient oil adhesion; this means that the risk of ring and piston seizures and/or scoring increases as the area of these polished surfaces increases.
Ring-shaped inserts serving such a function were disclosed by the German Pat. No. 30 38 235 and the German preliminary Pat. No. 19 00 922 corresponding to U.S. Pat. No. 3,489,130--Polidan et al dated Jan. 13, 1970. However, these disclosures fail to provide simple and, at the same time, secure fastening, i.e., among other things, easy installation in, or removal from, the cylinder liner. The press fit or shrink fit of the insert described in the prior art in a recess of the liner on the one hand makes removal of the insert difficult, and, moreover, involves the danger of the insert loosening under thermal stress due to upsetting.
The latter applies also where, for instance, the insert is made of a material having a coefficient of expansion that is somewhat greater than that of the material of the cylinder liner (see German preliminary Pat. No. 19 00 922 corresponding to U.S. Pat. No. 3,489,130--Polidan et al dated Jan. 13, 1970). Furthermore, the recess provided in the liner area weakens the upper cross-sectional area of the liner. Where the insert is fitted by straight overlapping (form-locking closure), which is also described in the German preliminary Pat. No. 19 00 922, corresponding to U.S. Pat. No. 3,489,130--Polidan et al dated Jan. 13, 1970, via a lip on the cylinder head, an oscillating movement of the insert in the micro range is inevitable; where forced-locking fitting is adopted, the load is applied to the insert, and failure or separation of the liner flange or breaking away thereof can occur.
Therefore, the object of the present invention is to simplify and improve the attachment of the insert in a cylinder liner of the aforementioned general type in such a way that, in addition to easy installation and removal of the insert, no weakening of components (i.e. no weakening of the upper liner area) results and no loosening of the insert develops during operation.